FAILED: patch "[PATCH] powerpc/pseries: Fix xive=off command line" failed to apply to 5.1-stable tree

The patch below does not apply to the 5.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a3bf9fbdad600b1e4335dd90979f8d6072e4f602 Mon Sep 17 00:00:00 2001
From: Greg Kurz <[email protected]>
Date: Wed, 15 May 2019 12:05:01 +0200
Subject: [PATCH] powerpc/pseries: Fix xive=off command line
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On POWER9, if the hypervisor supports XIVE exploitation mode, the guest OS will unconditionally requests for the XIVE interrupt mode even if XIVE was deactivated with the kernel command line xive=off. Later on, when the spapr XIVE init code handles xive=off, it disables XIVE and tries to fall back on the legacy mode XICS.

This discrepency causes a kernel panic because the hypervisor is configured to provide the XIVE interrupt mode to the guest :

kernel BUG at arch/powerpc/sysdev/xics/xics-common.c:135!
...
NIP xics_smp_probe+0x38/0x98
LR xics_smp_probe+0x2c/0x98

  Call Trace:
    xics_smp_probe+0x2c/0x98 (unreliable)
    pSeries_smp_probe+0x40/0xa0
    smp_prepare_cpus+0x62c/0x6ec
    kernel_init_freeable+0x148/0x448
    kernel_init+0x2c/0x148
    ret_from_kernel_thread+0x5c/0x68

Look for xive=off during prom_init and don't ask for XIVE in this case. One exception though: if the host only supports XIVE, we still want to boot so we ignore xive=off.

Similarly, have the spapr XIVE init code to looking at the interrupt mode negotiated during CAS, and ignore xive=off if the hypervisor only supports XIVE.

index bab79c51ba4f..17f1ae7fae2c 100644
@@ -172,6 +172,7 @@ static unsigned long __prombss prom_tce_alloc_end;
 
 #ifdef CONFIG_PPC_PSERIES
 static bool __prombss prom_radix_disable;
+static bool __prombss prom_xive_disable;
 #endif
 
 struct platform_support {

@@ -808,6 +809,12 @@ static void __init early_cmdline_parse(void)
 	}
 	if (prom_radix_disable)
 		prom_debug("Radix disabled from cmdline\n");
+
+	opt = prom_strstr(prom_cmd_line, "xive=off");
+	if (opt) {
+		prom_xive_disable = true;
+		prom_debug("XIVE disabled from cmdline\n");
+	}
 #endif /* CONFIG_PPC_PSERIES */
 }
 

@@ -1216,10 +1223,17 @@ static void __init prom_parse_xive_model(u8 val,
 	switch (val) {
 	case OV5_FEAT(OV5_XIVE_EITHER): /* Either Available */
 		prom_debug("XIVE - either mode supported\n");
-		support->xive = true;
+		support->xive = !prom_xive_disable;
 		break;
 	case OV5_FEAT(OV5_XIVE_EXPLOIT): /* Only Exploitation mode */
 		prom_debug("XIVE - exploitation mode supported\n");
+		if (prom_xive_disable) {
+			/*
+			 * If we __have__ to do XIVE, we're better off ignoring
+			 * the command line rather than not booting.
+			 */
+			prom_printf("WARNING: Ignoring cmdline option xive=off\n");
+		}
 		support->xive = true;
 		break;
 	case OV5_FEAT(OV5_XIVE_LEGACY): /* Only Legacy mode */